The present invention relates to a detector for analyzing the condition of the heart and is used in conjunction with a device capable of electrically stimulating a heart experiencing ventricular fibrillation, ventricular tachycardia, supraventricular tachycardia, or other arrhythmias. Specifically, the present invention relates to a detector capable of discriminating ventricular fibrillation (VF), polymorphoric ventricular tachycardia (PVT) from other arrhythmias of the heart and discriminating ventricular tachycardia (VT) from tachycardia of supraventricular origin. The present invention also relates to a unique delta modulator that operates on the ECG signal.